We propose to study some aspects of the response properties of single cells in the dorsal cochlear nucleus (DCN) and inferior colliculus (IC) as well as the organization of the connections between the cochlear nucleus and the IC. Studies of the DCN in decerebrate cats have shown that its cells are very sensitive to anesthesia. We will study the responses to sound of cells in the DCN in awake, intact cats, both in quiet and in the presence of background noise. Multiple-unit recordings will be used to study the internal organization of this nucleus. Electrical stmulation of the afferent and efferent fiber tracts of the IC will be used to study the interaction within the IC of ascending activity from different parts of the cochlear nucleus and to differentiate the response patterns of Golgi type II cells from the response patterns of cells whose axons project out of the IC. Knowledge of the connectivity of IC cells should be of value in trying to infer the functional significance for hearing of their response patterns.